The CCNet resource pack includes custom armour textures that can be activated by renaming armour items in a certain way.
To see these textures, you need to install Optifine or the CITResewn mod for Fabric.
American
for the USAAustro
for the Austro-Hungarian EmpireBelgian
for BelgiumBritish
for BritainFrench
for FranceGerman
for the German EmpireJapanese
for JapanOttoman
for the Ottoman EmpireRussian
for the Russian EmpireItalian
for the Kingdom of ItalyFinnish
for FinlandCultistIron
CultistGold
CultistDiamond
CultistNetherite
Cultist
You can change the texture of leather horse armour by dyeing it a specific colour. Unlike player armour, this does not require Optifine or CITResewn - the CCNet resource pack itself is sufficient.